The Indian government has said Pakistan will be given evidence that its spy agency, ISI, was behind the July train blasts in Mumbai that killed 186.
Seven blasts hit Mumbai's busy commuter network
Mumbai police arrested four people and on Saturday said the attacks were carried out by Pakistan-based Islamist militant group Lashkar-e-Toiba.
Pakistan quickly denied the accusation as "baseless" and demanded proof.
Analysts say the war of words may mean that the recent moves to revive the peace talks may suffer a setback.
More than 1,000 people were wounded in the blasts.
Deeds, not words
"We will take the issue up with Pakistan in view of new evidence," Indian Foreign Secretary Shiv Shankar Menon said without specifying.
"We will judge them [Pakistan] not by their immediate reaction of verbal statements, but by what they actually do about terrorism," Mr Menon said.
He said India wanted Pakistan to "not only talk, but act too".
India postponed peace talks with Pakistan after the bombings, but Indian Prime Minister Manmohan Singh and Pakistani President Pervez Musharraf met recently in Cuba and said they had agreed to resume the negotiations.
The two sides agreed to set up a joint mechanism to fight terror and the foreign secretaries of the two countries are due to meet in Delhi later in November to discuss the issue.
On 11 July 2006, seven co-ordinated blasts within 15 minutes ripped through trains on Mumbai's busy commuter network.
Mumbai (Bombay) police commissioner AN Roy told a news conference on Saturday that the authorities had "solved" the case.
The Mumbai police chief said the 11 July case was "solved"
"The whole attack was planned by Pakistan's ISI and carried out by Lashkar-e-Toiba and their operatives in India," he said.
He said the Students' Islamic Movement of India had also assisted.
Mr Roy said 11 Pakistanis were involved in the operation, and had crossed into India in small groups from Pakistan, Nepal and Bangladesh.
Tariq Azim Khan, Pakistan's Minister of Information, rejected the allegations.
"We are still studying the Indian statement. Needless to say, this is once again baseless allegations - yet another attempt by India to malign Pakistan," he told the BBC.
"Both the president and the prime minister condemned this terrorist attack on the train when it happened. But India also must look at home for reasons for this growing insurgency at home," he said.
Lashkar-e-Toiba, a leading militant group fighting in Kashmir and based in Pakistan, has condemned the attacks.